The present invention relates to methods and apparatus for transmission of laser radiation without loss of spatial coherence. More particularly, the present invention relates to a wave guide for transmission of laser radiation which represents a significant improvement over the hollow rectangular wave guide disclosed in Bass et al. U.S. Pat. No. 4,068,920 issued Jan. 17, 1978.
Fiber optic wave guides are presently employed for conduction of laser radiation in the visible portion of the spectrum. Optical fibers are flexible and permit pointing and focusing of visible light. Instruments which include optical fibers are widely used in the fields of medical diagnosis and treatment. While fiber optic wave guides may be satisfactory for conduction of visible light, they are not suitable for transmission of infrared laser radiation because of large losses which occur at 10.6 .mu.m.
Presently used surgical and industrial techniques for flexible delivery of infrared laser radiation to a target rely upon articulated arm systems of rotatable mirrors. Devices based upon articulated arm systems are bulky and delicate and cannot be manipulated as easily as fiber optic devices.
A hollow rectangular flexible infrared transmissive wave guide capable of transmitting more than 95% of incident 10.6 .mu.m laser radiation for distances of 1 to 10 meters is described in Bass et al. U.S. Pat. No. 4,068,920 issued Jan. 17, 1978. The hollow synclastic shape of the wave guide of the present invention enhances preservation of spatial coherence of the laser beam in transmission compared with the hollow rectangular shape of the Bass et al. wave guide.
A hollow cylindrical wave guide for transmission of laser radiation is disclosed in Marcatilli et al., U.S. Pat. No. 3,386,043 issued May 28, 1968. Applicants' invention relies upon the discovery that a synclastic wave guide preserves spatial mode coherence of laser radiation directed tangentially along an inner surface of the guide. Because the Marcatilli et al. wave guide depended upon waves filling an entire cylinder rather than being guided along an inner surface, their guide was thought to attenuate laser waves so severely upon bending that wave guides bent with a radius of curvature of less than 48 meters would be impractical.
It is a principal object of the present invention to provide a synclastic wave guide having a generally oval cross-section, for transmission of spatially coherent infrared laser radiation without loss of spatial coherence.
It is a related object of the present invention to provide a method for using the synclastic wave guide of the invention.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification, taken in conjunction with the drawings.